Belts

Minimum two: black leather for formal, brown leather for everyday. A third in tan or cognac bridges the gap. Match belt colour to shoe colour, it's the traditional rule and it works. Two belts, done properly, cover 95% of situations.

Full-grain leather (not "genuine" leather, which is actually a lower grade). Even, tight stitching. Substantial hardware that operates smoothly. A good leather belt develops a patina with age, it looks better over time, not worse. This is one category where preloved can actually be an upgrade.

5-7cm longer than your trouser waist size. So 32-inch waist, 34-inch belt. The tail should reach the first loop past the buckle. You should be using the middle hole, if you're on the first or last, the size is wrong.